Positioning of a video head is an important factor in determining the quality of the information that can be written on a magnetic tape. Especially, when a plurality of video heads are used for recording, each of the video heads should be positioned at a precise location so as not to adversely influence each other. For example, in a VCR of a video home system (VHS) incorporating therein two video heads, each of the video heads is located in a symmetric position with respect to the central axis of a rotary drum and on the same plane perpendicular to the enteral axis. If any one of the video heads deviates from the plane by some amount, the preceding magnetism pattern is overwritten by the following magnetism pattern, or a large gap is formed between tracks. In both cases, the recorded magnetism pattern is unevenly formed on a videotape, resulting in a degradation of the signals reproduced from the recorded magnetism pattern.
In FIG. 1, there is shown one of the head drum assemblies employing a conventional video head. The head drum assembly 1 includes a rotary drum 3, a video head 5 composed of a head chip 7 and a base plate 9 for mounting the head chip 7 thereon (see FIG. 2) and a stationary drum 11.
The rotary drum 3 is provided with a base plate fixing screw 13 for fixing the base plate 9 to a lower surface thereof and a set screw 15 for adjusting a vertical position of the head chip 7. The rotary drum 3 is fixed to a flange 17 by a rotary drum fixing screw 21. The flange 17 is provided with a rotor transformer 19a fixed by an adhesive or the like on a lower surface thereof and a rotating shaft 23 closely fitted thereinto. On the other hand, a stator transformer 19b is fixed on a top surface of the stationary drum 11 in such a way that a gap is created between the rotor and the stator transformers 19a and 19b.
In assembling the prior art head drum assembly 1, as shown in FIG. 2, the base plate 9 is fastened to the lower surface of the rotary drum 3 through the rotary drum fixing screw 21 so that the outer side of the head chip 7 may protrude beyond past the peripheral surface of the rotary drum 3 by a predetermined length. Then, the set screw 15 is fastened from top of the rotary drum 3 through a threaded hole 25 formed at the rotary drum 3, to thereby adjust the vertical position of the head chip 7.
In such a head drum assembly, however, it is difficult to adjust the vertical position of the head chip precisely, since it is manually adjusted.